A misconception is that the Expiry Time setting dictates how long a VoIP conversation can last. That is incorrect. The expiry time settings indicates to the router how often it should re-register with the SIP server. The expiry time setting on the router should be less than or equal to the value specified by your VoIP Provider. If the expiry time setting is set incorrectly, the DrayTek router may lose registration status with the SIP server.